An aim of agriculture since the earliest of times has been to enhance the capacity of agricultural crops. Various activities have been undertaken to enhance the growth rate and yield of plants and the quality of the crop produced. Various fertilisers have been used ranging from various animal manures to relatively purified chemical substances to assist the delivery of elements required for plant growth.
It has long been recognised that in addition to carbon, oxygen and hydrogen, various elements are required in relatively different amounts to achieve enhancement of plant capacity. Those elements required in relatively larger amounts are usually designated the major nutrients which are usually subgrouped further into those of greatest requirement; nitrogen, phosphorous and potassium and a second group; sulphur, calcium, magnesium, sodium and chlorine. The elements which were found to be required in relatively smaller amounts are usually designated the trace elements of which the principal ones are copper, zinc, manganese, iron, boron and molybdenum.
Furthermore it has been recognised that crops have two general states of requirement of the major elements. Firstly, plants must absorb sufficient of an element, supplied by fertiliser application if necessary, to alleviate symptoms resulting from a deficiency of supply of the element. Secondly, crops may be further enhanced by positive responses of growth rate, yield and quality resulting from the supply to and absorption by the plant of quantities of elements exceeding those required to alleviate symptoms of deficiencies. Plants growing in this second state will have generally been supplied with sufficient of all the major elements to remove them from a condition of deficiency.
It has also long been recognised that in certain soil types and for certain plants symptoms of deficiencies are linked to an under supply of various trace elements. A practice has developed to diagnose these deficiencies and address specific instances of trace element insufficiency as they occur by supplying additional quantities of one or more trace elements.
The various formulations of nutritional substances used to deliver prescribed quantities of major elements and address specific instances of diagnosed deficiencies of trace elements are generally applied directly to the soil or solubilised (or suspended) for foliar application. The application by foliar fertilisation reduces the risk of any elements within the nutritional substance being complexed with a constituent of the soil, thereby allowing a more accurate application of required elements and avoiding ineffectual applications of components of the fertilising substance. As a consequence, fertilising substances containing trace elements applied to soil tend to be quite different from those used for foliar application and are focussed towards generally changing the availability of a trace element in a particular soil rather than primarily focussing upon the trace element nutrition of a particular crop. The complexing of trace elements with soil constituents and physical dispersal within a soil dictates that applications to soil are usually an order of magnitude greater per area than for foliar fertlisers.
A limitation of foliar application of nutritional substances is the maximum rate of a specific substance which can be applied without causing leaf tissue damage.
The application of trace elements to agricultural crops has been largely to prevent further appearance of or to rectify an actual trace element deficiency and has not been used in the more general sense to enhance crop yield or quality characteristics of specific crops in conditions where trace element deficiencies have been counteracted or in conditions which are regarded as generally favourable for the growth of particular crops in terms of being sufficient in trace elements.
Some fertilisers do incorporate multi trace element combinations as an adjunct but at relatively low levels. A number of others use multi trace element supplements in very atypical circumstances such as where soil-less media are used. A number of patent disclosures are pertinent to such situations. U.S. Pat. No. 4,455,161 to Cohen et al is a multi trace element formulation particularly useful for potted plants in a soil-less medium. Cohen proposes formulations which do not contain boron and specify an iron : manganese ratio which is not necessary for effective foliar fertiliser formulations, and also which require gypsum. U.S. Pat. No. 4,328,025 to Whitcomb also relates to a multi trace element mixture. The formulations disclosed specify a higher proportion of iron for a plant growing in medium for container grown plants than the compositions of the present invention.
Other documents relate to foliar fertilisers and are often concerned with aspects of maintaining solubility. U.S. Pat. No. 4,505,732 to Aigner et al is concerned with the manner in which combinations of trace elements and the secondary major element, magnesium, can be maintained in soluble form to redress deficiencies and inadequate supply of magnesium and the trace elements, manganese and boron in particular. A proposed formulation was partially successful in relieving manganese deficiency in plants grown in a soil of known lower status for manganese supply. U.S. Pat. No. 4,395,273 to Leutner et al relates to a simple process for preparation of multi trace element fertlisers containing magnesium and including chelates of N-carboxyalkylaminoacids as a means of facilitating the preparation of the multi trace element formulation. This specification does however not disclose elevated application rates, nor is the efficacy of the compositions tested. U.S. Pat. No. 5,514,201 to Marijuan De Santiago et al. discloses the process for forming a deficiency correcting substance containing magnesium and principally three trace elements (iron, manganese and zinc) but it contains no boron or molybdenum.
To the best knowledge of the present inventors there has been no disclosure of a foliar fertilising composition or method of fertilising that provides beneficial effects which are substantially independent of the soil type and that give a substantially consistent enhancement in a large range of crops and across cultivars of a crop.